This invention relates to apparatus for performing electrophoresis. In particular, this invention relates to an apparatus for supporting a vertical gel or a series of such gels together with the buffer solutions necessary for the electrophoretic separation of samples along the gels in the vertical direction.
Gel electrophoresis is a widely used and highly effective technique for separating complex mixtures of chemical species. It is useful for both analytical and preparatory purposes, and is well-known for its unique ability to separate complex chemical species such as proteins, polypeptides, nucleic acids and oligonucleotides. It receives particularly wide use in the biotechnology industries.
In both tube gels and slab gels, electrophoresis is frequently done with the gel in the vertical or upright position. This facilitates the insertion of samples at one end (the top end of a tube gel or the top edge of a slab gel), and also facilitates the immersion of the top and bottom ends in appropriate buffer solutions.
This arrangement has its problems, however. Since two buffer solutions are involved, they are frequently at different heights and must be sealed off from each other to prevent leakage between themselves. Many cell structures have been designed which prevent such leakage, but are awkward to use. For example, the laboratory technician is normally called upon to cast the gel, then seal it into the cell assembly so that when the buffers are added there is full contact with the edges of the gel yet no leakage, then add the samples, add the buffer solutions, and run the separation, then disassemble the entire apparatus and prepare it for the next run using a newly cast gel and a new set of samples. Each assembly or disassembly step is prone to human error, raising the possibility of leakage, and the overall procedure is complicated and lengthy. In addition, tube gels and slab gels, due to their different geometries, generally required separate pieces of equipment, each designed exclusively for one or the other.
In either type of gel geometry, one of the most critical parts of the procedure in assembling a vertical cell is containing and sealing the upper buffer solution in a manner which will prevent it from leaking down into the lower buffer solution. In sandwich-type slab gel assemblies (in which the gel is cast between two flat plates), this problem is partially solved by using plates of unequal height. The taller plate thus extends above the upper edge of the gel slab and acts as one wall of the chamber which contains the upper buffer solution. Nevertheless, it remains difficult to join the remaining walls of the buffer chamber to the gel plate assembly in a leak-proof manner.
Sandwich-type slab gel assemblies using plates of unequal height present a further sealing problem, i.e., forming lateral seals to enclose the space above the gel. This problem is particularly acute when the plates are designed to be separated and reassembled by the user in between each use. One attempt to overcome this is the use of a notched plate as the shorter plate--i.e., having a single long notch in the center extending for the entire width of the gel, the ends of the plate being the same height as the taller plate. Examples are those supplied by Hoefer Scientific Instruments, San Francisco, Calif., as part of its Vertical Slab Electrophoresis Unit SE-500; and those disclosed by F. W. Studier in "Analysis of Bacteriophage T7 Early RNAs And Protein On Slab Gels," J. Mol. Biol., 79, 237-248 (1973). Since the plates are usually made of glass, however, notched plates are expensive to make and the upward extensions on each side are easily broken.